“…One of the main reasons for the differences in girls' values of 9 and 10 years in favor of the latter is related to the morphosis (Malina, Bouchard, Bar-Or, 2004). During this period the physiological characteristics and physical fitness of the child are improved with each new year of his/her life (Astha, 2011;Bar-Or, Rowland, 2004;Carlos, Daniel, Marques, 2012;Delas, Lafreničre, Fenouillet, Paquet, Martin-Krumm, 2017). The high level of development of the body's systems, in turn, contributes to a better solution of various tasks that the coach puts in the initial stage of young athletes' training (Dick, 2007;Raiola, 2014;Sally, 2004).…”